1. Field of the Invention
The present invention relates to a silver halide color photographic material, in particular to a silver halide color photographic material of good whiteness. The invention also relates to a method of image formation on the silver halide color photographic material.
2. Description of the Related Art
With the popularization of digital cameras and personal computers in recent years, the frequency of using silver halide photographic materials in printing digital image information thereon is increasing. Image printing materials other than silver halide photographic materials, such as those for inkjet printers are now in wide use for printing digital image information thereon. In order that silver halide photographic materials such as color printing paper are competitive with those printing materials, they are much desired to be more rapidly and stably processed to form high-quality images thereon.
In particular, the recent improvement in the image quality of image printing materials except silver halide photographic materials is remarkable, and it is much desired to further improve the quality of silver halide photographic materials in order that they are competitive over the recent image printing materials. To improve the image quality of silver halide photographic materials, one important factor is to improve couplers to thereby improve the hue of color dyes formed. In addition, it is well known in the art that another important factor is to increase the degree of whiteness of the background area of the photographic materials, or that is, to improve the density and the tone of the non-exposed portion of the materials. If the whiteness of the background area of photographic materials is low, it lowers and worsens the brightness and the tone of the highlight area of the materials, often causing color mixing in the area that contains different color dyes to worsen the images formed. If so, in addition, the image contrast is visually lowered in the area composed of a non-colored part and a colored part. The whiteness is especially important in the background area of photographic materials, such as color paper, on which the images formed are directly seen as they are.
To obtain photographic materials of good whiteness, it is important to prevent silver halides from being fogged, and to specifically plan photographic materials so that the coloring matters such as sensitizing dyes do not remain in the processed photographic materials. To achieve this, various investigations have been made in the art, for example, as in JP-A 6-39936, 6-59421, and 6-202291. In particular, it is important that silver halides in photographic materials are not fogged not only just after the photographic materials are produced but also while the photographic materials produced are stored before being exposed and processed. To prevent photographic materials from being fogged while they are stored, for example, it is known to add an antifogging agent thereto as in JP-A 62-215272; to add catechol or hydroquinones as in JP-A 11-143011; and to add a water-soluble reducing agent of formulae (I) to (III) as in JP-A 11-102045.
Another method known for improving the quality of the white background area of photographic materials is to prevent photographic materials from being stained with the processing solutions used for processing them, or to add to photographic materials some coloring matters complementary to the unnecessary colors therein to thereby control and neutralize the color in the background area of photographic materials.
The quality of color paper just after production is a matter of importance, but the quality stability thereof not changing in time while stored before exposed and processed is also important. In particular, the change in the white background area of color paper is often striking, and this is the most important matter that color paper does not fog during storage.
When processed rapidly, photographic materials are subjected to high-temperature, high-activity treatment and are often fogged, and in addition, sensitizing dyes often remain in them and unfavorably color their background area. Therefore, it is especially desired to improve the quality of the white background area of photographic materials to be processed rapidly.
Given that situation, we, the present inventors have assiduously studied and have found that the emulsions obtained in the prior art mentioned above are still unsatisfactory. In particular, when the photographic materials that have been heretofore proposed, as in the above, are stored for a long time, the blue-sensitive emulsion layers therein are significantly fogged and the yellow density in the background area therein increases.
Through our further studies, it has been found that the yellow density increase in the background area of photographic materials is not expected in the forced heat test which we carried out for estimating the fog level of stored photographic materials, and that the fog density increase in photographic materials exposed to X rays corresponds to the relative correlation to the fog level of yellow, magenta and cyan in the photographic materials actually stored for a long time. From these findings, it is presumed that the yellow density increase in the background area of photographic materials will be caused by exposure to natural radiations and therefore the fog increase could not be evaded by the prior art techniques mentioned above.
In particular, the yellow density increase is remarkable in photographic materials which are designed to lower the density of the white background area thereof so as to control the whiteness of that area to a desired level. In other words, even when the yellow density increase that results from the fog increase in the blue-sensitive emulsion layers is on the same level in different photographic materials, the color change in the white background area of photographic materials of which the whiteness is not increased is not so striking and is on the acceptable level, while, on the other hand, the yellow density increase in photographic materials of which the whiteness has been increased is more striking and, as a result, it lowers the whiteness of the photographic materials. Accordingly, it is desired to develop photographic materials having a desired degree of whiteness not only immediately after their production but also during and after storage thereof.
In addition, it is also desired to develop silver halide color photographic materials of high sensitivity, of which the gradation characteristics are good in that the shoulder contrast is lowered little even when the exposure time for them is short.